Transformer



1960 J. KOWATSCHITSCH ETAL 72,960,672

TRANSFORMER Filed May 18, 1959 III III III] III/ II,

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INVENTORS JOSEF KOWATSCHITSCH a ALFRED LEHMANN AGENT United StatesPatentO TRANSFORMER Josef Kowatschitsch and Alfred Lehmann, Weiz,Styria,

Austria, assignors to Elin Aktiengesellschaft fiir elektrischeIndustrie, Vienna, Austria Filed May 18, 1959, Ser. No. 813,835

Claims priority, application Austria May 21, 1958 1 Claim. (Cl. 336-58)This invention relates to electrical transformers and more particularlyto an exhaust valve ventilating gas bubbles resulting from tap changingunder load.

It is a known method to protect the oil in a transformer tank or in itsexpansion tank above the tank by filling the space above the oil levelwith an inert gas, usually nitrogen, preventing in such a way thedeterioration of the oil quality by absorption of oxygen, hydrogen andmoisture from the outside air. In transformers being adjustable underload, furthermore, it is known to sep arate the oil in the transformertank from the oil of the transfer switch as this latter oil may becontaminated by the effects of the switching arc (gas bubbles, contactburning off). If the on-load tap changers are incorporated in thetransformer unit, as usual, the selector switch and the transfer switchare assembled into one tube-shaped unit which is sunk into thetransformer tank. The transfer switch, however, is contained in aseparate oil-tight enclosure to prevent communication of the transformeroil with the oil of the transfer switch. For the same purpose, theexpansion tank contains a separate compartment for the expansion of thetransfer switch oil. Gases due to the switching arc may escape throughthis compartment to the open. This contact of the transfer switch oilwith the outside air, however, is disadvantagzous by two reasons. Firstof all, it is diflicult to seal the transfer switch compartment againstthe surroundlng transformer oil to a satisfying extent, because the gaspressure resulting from fluctuations in oil temperature (caused by loadvariations) may rise considerably so that an overflow of tank oil intothe transfer switch compartment may always occur. Of late there ismoreover a trend to protect also the transfer switch oil from absorptionof oxygen, hydrogen and moisture from the outside air. Therefore, alsothe oil level in the expansion tank compartment belonging to the on loadtaps changer has been covered with an inert gas by providing an openingin the dividing wall of the expansion tank lying above the maximum oillevel, enabling in such a way to access of the inert gas from theexpansion tank compartment be'onging to the transformer tank to the oillevel of the transfer switch. In doing so also the transfer switch oilis protected from the access of oxygen, hydrogen and moisture. Likewisethe pressure differences between the transformer tank and the transferswitch compartment are equalized. It is a disadvantage, however, that insuch a case the gas bubbles resulting from the switching are mix withthe inert gas and soil it and influence the rate of pressure of theinert gas cushion.

Therefore it is the object of this invention to show a way forventilating gas bubbles resulting from tap changing under load Withoutthe above indicated disadvantages.

This invention will be better understood from the following descriptiontaken in connection with the accompanying drawing.

In the drawing Fig. 1 is a simplified view illustrating a transformertank (partly represented only), its expansion 2,960,672 Patented Nov.15, 1960 tank (likewise partly represented only) and the connectingpipes between the tank and the expansion tank. Fig. 2 shows theventilating valve on an enlarged scale.

Referring now to the drawing and more particularly to Fig. 1 there isshown therein a transformer tank 1 receiving the active parts of thetransformer 2 (core and windings) and the on-load tap changer consistingof selector switch 3 and transfer switch 4. As indicated, the transferswitch 4 is enclosed in a separate casing whilst the selector switch issurrounded by the transformer tank oil, as a rule. The expansion tank 5is subdivided by a wall 6 into a compartment for the transformer tankoil and a smaller compartment for the transfer switch oil. 7 is the oilpipe from the expansion tank to the transformer tank and 8 is the oilpipe to the transfer switch casing. In accordance with this invention,an exhaust valve 9 is inserted into the latter. The wall 6 dividing theexpansion tank has an opening above the highest oil level that might bereached. The space 10 of the expansion tank above the oil level isfilled in known manner with an inert gas having a fluctuating pressure.

In Fig. 2 which shows the exhaust valve according to this invention insection on an enlarged scale, 11 indicates a float chamber. This floatchamber is inserted into the oil pipe 8 to the transfer switch byflanges 12, 13, and that in such a manner that gas bubbles coming fromthe transfer switch casing gather in the upper part of the floatchamber. 14 is a float the buoyant force of which in the oil istransmitted by an one-armed lever 15 to a valve disk 16. The latter isguided in a valve casing 18 fixed to the cover 17 of the float chamber11 and cooperates with the valve case 19. An outlet connecting piece 21is fitted to the valve case 19 by the screw cap 20. 22 is a guiding rodfor the float and 23 an oil gauge atttched to the float chamber. As itis seen from the drawing, the buoyant force of the float is geared intoa high contact pressure of the valve disk.

The operation of the exhaust valve according to this invention is asfollows. Before a stepping action, the oil level in the float chambermay stand as high as indicated by the level marker (V) in Fig. 1). Withsuch an oil level the float is subjected to a certain buoyant force. Thelatter acts in a geared rate upon the valve disk and closes the valve.Supposing that gas bubbles result from a stepping action, the gasbubbles will gather in the upper space of the float chamber and willdepress the oil level. In doing so the buoyant force becomes lower. Ifthe oil level has sunk sufliciently so that the weight of the swimmerexceeds the buoyant force the valve opens and lets out so many of thegathered gas bubbles that the oil level existing before the switchingaction is restored and the outlet valve closes again.

In this way it is avoided that gas bubbles resulting from switchingreach the expansion tank compartment belonging to the transfer switch.Therefore, the cushion of inert gas may be common for both the expansiontank compartments without running the risk of deteriorating the inertgas and influencing the pressure in the gas cushion. Furthermore, indoing so equal pressure is reached in the transfer switch casing and inthe transformer tank, and therefore, the difliculties with regard to thesealing of the transfer switch casing against the surroundingtransformer oil are minimized. There is avoided, moreover, the loss ofinert gas resulting from the blowoff of the mixture of the switching gasand the inert gas being necessary from time to time if the switching gasmixes with the protecting inert gas.

What is claimed as neW and desired to secure by Letters Patent of theUnited States is:

In combination a transformer tank including a transformer core and itswindings, an on-load tap changer sunk in said transformer tankconsisting of the selector switch and the transfer switch, the latterbeing enclosed in a sep arate casing, an expansion tank subdivided by awall into one compartment for the transformer tank oil and onecompartment for the oil of the transfer switch casing, the space overthe oil levels in said expansion tank compartments being filled with aninert gas, oil pipes leading from the transformer tank and the transferswitch casing to the expansion tank, an exhaust valve being insertedinto the oil pipe leading from the transfer switch casing to theexpansion tank, for exhausting gas bubbles ascending 10 from thetransfer switch casing, said exhaust valve con- References Cited in thefile of this patent UNITED STATES PATENTS 2,915,720 Mueller Dec. 1, 1959FOREIGN PATENTS 162,526 Austria Mar. 10, 1949

